Little is known about his childhood. Around 1549-1550 he briefly visited Italy and likely spent a few months attending lectures at the Padua University.[1] Upon his return, he joined the army of Ferdinand I, Holy Roman Emperor, and took part in his military struggle against the Turks.[1] Some time after 1553 Báthory was captured by the Turks, and after Ferdinand I refused to pay his ransom, Báthory joined the opposing side, supporting John II Sigismund Zápolya in his struggle for power in the Eastern Hungarian Kingdom.[1] As Zápolya's supporter, Báthory acted both as a feudal lord, military commander and a diplomat.[1][2] During one of his trips to Vienna he was put under house arrest for two years.[2] During this time Báthory fell out of favour at Zápolya's court, and his position was largely assumed by another Hungarian noble, Gáspár Bekes.[2] Báthory briefly retired from politics, but he still wielded considerable influence and was seen as a possible successor to Zápolya.[2]

After Zápolya's death in 1571, the Transylvanian estates elected Báthory Voivode of Transylvania.[2] Bekes, supported by the Habsburgs, disputed his election, but by 1573 Báthory emerged victorious in the resulting civil war and drove Bekes out of Transylvania.[2] He subsequently attempted to play the Ottomans and the Holy Roman Empire against one another in an attempt to strengthen the Transylvania position.[3]

In 1572, the throne of the Polish-Lithuanian Commonwealth, at the time the largest and one of the most populous states in Europe, was vacated when King Sigismund II of Poland died without heirs.[3] The Sejm was given the power to elect a new king, and did so by choosingHenry of France; Henry soon ascended the French throne and forfeited the Polish one by returning to France.[3] Báthory decided to enter into the election; in the meantime he had to defeat another attempt by Bekes to challenge his authority in Transylvania, which he did by defeating Bekes at the Battle of Sinpaul.[3]

Báthory's position was at first extremely difficult, as there was still some opposition to Báthory's election. Emperor Maximilian, insisting on his earlier election, fostered internal opposition and prepared to enforce his claim by military action.[7] At first the representatives of the Grand Duchy of Lithuania refused to recognize Báthory as Grand Duke, and demanded concessions - that he return the estates of his wife Anne to the Lithuanian treasury, hold Sejm conventions in both Lithuania and Poland, and reserve the highest governmental official offices in Lithuania for Lithuanians. He accepted the conditions.[8] In June Báthory was recognized as Grand Duke of Lithuania, Duke of Ruthenia and Samogitia.[a][6][7]

With Lithuania secure, the other major region refusing to recognize his election was Prussia.[7] Maximilian's sudden death improved Báthory's situation, but the city of Danzig (Gdańsk) still refused to recognize his election without significant concessions.[7] The Hanseatic League city, bolstered by its immense wealth, fortifications, and the secret support of Maximilian, had supported the Emperor's election and decided not to recognize Báthory as legitimate ruler. The resulting conflict was known as the Danzig rebellion. Most armed opposition collapsed when the prolonged Siege of Danzig by Báthory's forces was lifted as an agreement was reached.[7][9] The Danzig army was utterly defeated in a field battle on 17 April 1577.[10] However, since Báthory's armies were unable to take the city by force, a compromise was reached.[10][11] In exchange for some of Danzig's demands being favorably reviewed, the city recognised Báthory as ruler of Poland and paid the sum of 200,000 zlotys in gold as compensation.[9][11] Tying up administration of the Commonwealth northern provinces, in February 1578 he acknowledged George Frederick as the ruler of Duchy of Prussia, receiving his feudal tribute.[9]

After securing control over Commonwealth, Báthory had a chance to devote himself to strengthening his authority, in which he was supported by his chancellorJan Zamoyski, who would soon become one of the king's most trusted advisers.[5][11] Báthory reorganised the judiciary by formation of legal tribunals (the Crown Tribunal in 1578 and the Lithuanian Tribunal in 1581).[12] While this somewhat weakened the royal position, it was of little concern to Báthory, as the loss of power was not significant in the short term, and he was more concerned with the hereditary Hungarian throne.[9][12] In exchange, the Sejm allowed him to raise taxes and push a number of reforms strengthening the military, including the establishment of the piechota wybraniecka, an infantry formation composed of peasants.[9] Many of his projects aimed to modernize the Commonwealth army, reforming it in a model of Hungarian troops of Transylvania.[13] He also founded the Academy of Vilna, the third university in the Commonwealth, transforming a prior Jesuit college into a major university.[14] He founded several other Jesuit colleges, and was active in propagating Catholicism, while at the same time being respectful of the Commonwealth policy of religious tolerance, issuing a number of decrees offering protection to Polish Jews, and denouncing any religious violence.[13]

In external relations, Báthory sought peace through strong alliances. Though Báthory remained distrustful of the Habsburgs, he maintained the tradition of good relations that the Commonwealth had with its Western neighbor and confirmed past treaties between the Commonwealth and Holy Roman Empire with diplomatic missions received by Maximilian's successor, Rudolf II.[15] The troublesome south-eastern border with the Ottoman Empire was temporarily quelled by truces signed in July 1577 and April 1579.[15] The Sejm of January 1578 gathered in Warsaw was persuaded to grant Báthory subsidies for the inevitable war against Muscovy.[9]

A number of his trusted advisers were Hungarian, and he remained interested in the Hungarian politics.[13] He wished to recreate his native country into an independent, strong power, but the unfavorable international situation did not allow him to significantly advance any of his plans in that area.[16] In addition to Hungarian, he was well versed in Latin, and spoke Italian and German; he never learned the Polish language.[13]

In his personal life, he was described as rather frugal in his personal expenditures, with hunting and reading as his favorite pastimes.[13]

Before Báthory's election to the throne of the Commonwealth, Ivan the Terrible of Russia had begun encroaching on its sphere of interest in the northeast, eventually invading the Commonwealth borderlands in Livonia; the conflict would grow to involve a number of nearby powers (outside Russia and Poland-Lithuania, also Sweden, the Kingdom of Livonia and Denmark-Norway). Each of them was vying for control of Livonia, and the resulting conflict, lasting for several years, became known as the Livonian War.[17] By 1577 Ivan was in control of most of the disputed territory, but his conquest was short-lived.[17] In 1578 Commonwealth forces scored a number of victories in Liviona and begun pushing Ivan's forces back; this marked the turning point in the war.[15] Báthory, together with his chancellor Zamoyski, led the army of the Commonwealth in a series of decisive campaigns taking Polotsk in 1579 and Velikiye Luki in 1580.[15]

In 1584 Báthory allowed Zamoyski to execute Samuel Zborowski, whose death sentence for treason and murder had been pending for roughly a decade.[12][19] This political conflict between Báthory and the Zborowski family, framed as the clash between the monarch and the nobility, would be a major recurring controversy in internal Polish politics for many years.[12][19] In external politics, Báthory was considering another war with Russia, but his plans were delayed to the lack of support from the Sejm, which refused to pass requested tax raises.[19]

Báthory's health had been declining for several years.[19] He died on 12 December 1586, scarcely three months after his wife Anna. A 1934 autopsy concluded that the cause of death was chronic kidney disease.[20] He had no legitimate children, though contemporary rumours suggested he might have had several illegitimate children. None of these rumours have been confirmed by modern historians.[20] His death was followed by an interregnum of one year. Maximilian II's son, Archduke Maximilian III, was elected king but was contested by the Swedish Sigismund III Vasa, who defeated Maximilian at the Byczyna and succeeded as ruler of the Commonwealth.[21]

Immediately after his death, he was not fondly remembered in the Commonwealth. Many nobles took his behavior in the Zborowski affair and his domestic policies as indicating an interest in curtailing the nobility's Golden Freedoms and establishing an absolute monarchy.[20] His contemporaries were also rankled by his favoritism toward Hungarians over nationals of the Commonwealth.[19] He was also remembered, more trivially, for his Hungarian-style cap and saber (szablabatorówka).[22]